Three types of compounds were synthesized from carbendazim, a benzimidazole derivative, which includes a group of esters at N1 prepared by treating carbendazim with isocyanates bearing ester groups I [R = NH(CH2)2CO2CH2CH3, NH(CH2)3CH3, NHC6H4CO2CH3, etc.] while carboxyalkyl-1,2,3,4-tetrahydro-s-triazino[1,2-a]benzimidazole-2,4-dione esters II [R = CH2CO2CH2CH3, CO2CH2CH3] formed by cyclization of these esters and related hydrophilic amides II [R = CH2C(O)NH(CH2)2OH, CH2C(O)NH(CH2)2OCH3] derived from II [R = CH2CO2CH2CH3]. The antitumor potencies of the N1 esters were in the range of 7 to 40 μM, which compares favorably with carbendazim, but their water solubilities were low. The s-triazine derivatives showed activity against pancreatic tumor cells and one of them II [R = CH2C(O)NH(CH2)2OH] was active in mice, but they were not effective against other tumor types. Treatment of carbendazim with 3-bromopropionyl chloride produced 1-methoxycarbonyl-4-oxo-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole, which gave 1-(3-aminopropionyl)benzimidazole 2-methylcarbamates, substituted on the amino nitrogen III [R = NH(CH2)2OCH3, morpholin-4-yl, NHCH2C6H5], when treated with amines. These products showed some antitumor activity in cell cultures, and an ethoxy derivative III [R = OCH2CH3], obtained by treating 1-methoxycarbonyl-4-oxo-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole with sodium ethoxide, was active in the 67-150 μM range. Some of the new compounds II and III had good water solubility Carbendazim kills tumor cells by inhibiting tubulin; however, s-triazine II [R = CH2C(O)NH(CH2)2OH], which differs from it in size and functional groups, does not act by this mechanism.